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Chapter 5: Circadian Rhythm Sleep Disorders

What is Non-24 Hour Sleep Wake Disorder?

Non-24-Hour Sleep Wake Disorder (“Non-24”) is characterized by an abnormal sleep-wake rhythm caused by a circadian clock that is not in phase with, and cannot be entrained to, the 24-hour light-dark cycle.51 (This disorder is also called “non-entrained type circadian sleep disorder” and “free-running circadian rhythm sleep disorder.”)

People with Non-24 “have periodically recurring problems with sleep initiation, sleep maintenance, and rising.”52 Patients complain of insomnia and excessive daytime sleepiness related to the abnormal synchronization between the person’s drifting sleep cycle and the normal sleep-wake schedule.53